Photo-conductor potential divider



Jan. 9, 1968' D. M. PARK 3,353,106

PHOTO-'CQNDUCTQR POTENTIAL DIVIDER Filed June 26, 1964 34 AUDIO VO LUI\/IE AUD'O TERMINAL RESISTANCE AMPLIFIER LIGHT POSITION 30 FIG. 2

' /8I AUDIO SIGNAL SOURCE 8O FIG/I FIG. 7

MIRROR IOBVOLTAOE FIG. 9

sOuRcE B T VOLTAGE 2 2 SOURCE 94 T2 71 2 30 INVENTOR. FIG 5 Donald M.Park BY 3O fi/fffi 7 FIG T ATTORNEY United States Patent 3,363,106PHOTO-CONDUCTOR POTENTIAL DIVIDER Donald M. Park, Raleigh, N.C.,assignor to The Seeburg Corporation, Chicago, 111., a corporation ofDelaware Filed June 26, 1964, Ser. No. 378,382 3 Claims. (Cl. 250209)ABSTRACT (3F THE DISCLOSURE An electric organ swell control employs apotential divider that is formed from two photo-conductor tubes whichare placed in series and physically fixed in a housing adjacent the footpedal. The audio signal voltage is applied across the divider andthrough a center tap, the audio signal or tone is fed to an audioamplifier. A light source mounts on the foot pedal which controls thetone and as the pedal moves the light from the source is directed towardthe housing and illuminates the tubes independently and in sequence soas to swell the tone.

This invention is concerned with an electrical device which acts as apotential divider and which employs a plurality of photo-conductiveelements in series, the illumination of which determines the manner inwhich the potential is divided. More specifically, the invention isconcerned with a potential divider useful as a swell or volume controlin electric organs and which can be made as a position sensitive device.

Heretofore, the pedal operated devices which have been used to increasedand decrease volume in electric organ instruments have principally beenmechanical with attendant undesirable noises that feed into the audiocircuits. Mechanical volume controls having moving contacts alsofrequently get out of adjustment. A potential divider electronic innature and utilizing a single photo conductor has been employed in theelectric organ art however the single photo conductor type isexceedingly slow in turn-off response time. In fact, photo-conductorsare inherently slow in turn-ofi response time and are not generallyconsidered for fast response or relatively fast response applications.Still another approach to position sensitive potential dividers fororgan pedal operation is illustrated in my prior Patent 3,042,888.

An object of the present invention is therefore to provide an electricalpotential dividing device whose output voltage can be controlled by someposition changing device such as an organ foot pedal.

Another object is to provide such a potential dividing device which whencombined in operation with audio circuitry is inherently noiseless.

Another object is to provide such a potential dividing device whichutilizes a plurality of photo-conductor elements in series and therebygains a relatively fast response.

Another object is to provide such a potential divider which is capableof producing either gradually changing or relatively rapid changingaudio control voltages as desired.

These and other objects of the invention will become apparent from thedescription and in the drawings, in which:

FIGURE 1 is a schematic diagram of a potential dividing circuitembodying the invention.

FIGURE 2 is an audio volume versus light position curve.

3,363,196 Patented Jan. 9, 1968 IGURE 3 illustrates the inventionapplied to a pedal control device.

FIGURE 4 is a schematic illustration of a second embodiment.

FIGURE 5 is a schematic illustration of a third embodiment.

FIGURE 6 is a front view of one of the elements of FIGURE 5.

FIGURE 7 is a schematic illustration of a fourth embodiment utilizing amodification of one of the elements of FIGURE 5.

FIGURE 8 is a schematic illustration of a fifth embodiment.

FIGURE 9 is a schematic illustration of a sixth emment.

The invention comprises in a broad sense an electrical potential dividerformed from a group of photo-conductor tubes placed in electricalseries, with a minimum of two tubes, and with means to illuminate eachtube independently of illuminating the other tubes to the same degree ofillumination. When a potential is placed across the divider, thepotential at a fixed center tap will vary as one or the other of thetubes are illuminated.

A number of forms of the invention will be described from which it canbe seen that the desired independent control of illumination on eachtube can be gained in various ways one of which is by relative change ofposition between a light source and the tubes. Such control ofindividual tube illumination can also be gained by stationing a fixedlight source opposite each photo conductor tube and then varying theintensity of the fixed light sources in difiering amounts such as byshading the light sources differently or by electrically varying theintensity of the light sources differently.

In FIGURE 1, a schematic diagram illustrates the invention in one of itsbasic forms and in which 20 represents a light source suitablyenergizing through conductors 21, 22. Light source 24) is arranged suchthat it can be physically moved along an arcuate path such as thatindicated at 23 and as it moves assume any of the indicated positions17. Fixedly positioned opposite light source 26 and at separate stationsthere is located a pair of photo conductor tubes 30, 31 which may forexample be type A35 made by General Electric Company of Schenectady, NY.Tubes 3 9, 31 in the example illustrated are connected in electricalseries between a typical audio signal source 32, which may be AC or DC,and ground at 33. An audio amplifier 34 is connected to a junction point35 between the photo conductor tubes 30, 31, it being desired to controlthe volume of audio amplifier 34 according to the physical position oflight source 20. Junction point 35 can be considered as being a fixedcenter tap on a potential divider comprising the series connected tubes39, 31 and across which appears such potential as is produced by signalsource 32.

As light source 21 approaches either of the tubes 30 or 31, in FIGURE 1it can be seen that the resistance of the tube so illuminated willdecrease radically assuming of course that light source 29 issufiiciently strong in illumination and sufficiently close to theindividual tube to achieve such result. As light source 20 moves forexample from say position 1 to position 7, the effective resistanceoffered audio signal source 32 between terminals T and T may besystematically reduced, with an appropriately designed circuit, insubstantially even graduations until minimum resistance between T and T'3 and maximum volume, corresponding to maximum potential at T areachieved.

The described result is generally illustrated in the curve 44) of FIGURE2. While illustrated as a linear curve, it will be'appreciated that inthe actual apparatus employing the invention as later discussed thisrelation may not in fact be linear. In any event, it should be notedthat as light source 20 moves toward tube 30, tube resistance willdecrease rapidly due to a very rapid turn-on time. At the same time,tube 31 resistance will be increasing in' view of a lessening ofillumination intensity on it. That is, the tubes are illuminateddifferentially or in differing amounts. However, the decay or turn-ofitime of tube 31 has substantially no influence on the volume changingtime since the turn-on time of tube 3-3 is much faster and asserts thegreater influence. Shading of the respective lamps as indicated at 41and 42 may assist in a sharper volume change when light source 2i) isplaced in motion.

FIGURE 3 illustrates an application of the invention to anvelectricorgan having a foot pedal 56 pivotally mounted on an axis 51 andsupporting at its free end a housing 52 bearing light source 28.Oppositely disposed to light source 20 is a fixed housing 53 mountingthe photo conductor tubes 30, 31 and being arranged for connection toterminals T T T indicated in FIGURE 1. According to the previousexplanation it can be seen that as pedal 50 pivots downwardly, thevolume of audio amplifier 34 can be made to increase or swell rapidly.

Of particular interest is the fact that theadvantages of the inventioncan be achieved in a variety of forms some of which are illustrated inthe remaining figures. In FIGURE 4 for example, there is a schematicillustration showing that the same etfect may be achieved by fixing thelight source 20 and arranging the housing represented by 53' (comparedto housing 53 seen in FIGURE 3) such that it can be moved along anarcuate path as represented at 60 in FIGURE 4. FIGURES 1, 3 and 4 thusbasically illustrate the concept of relative motion between the lightsource 26 and the photo conductor tubes 30, 31.

FIGURES 5, 6 and 7 schematically illustrate two other embodimentsutilizing a fixed light source. Both of these embodiments follow theconcept of having a moving member other than the light source or thephoto conductor tubes and which acts to vary illumination by variableshielding. In FIGURE 5, source 20 is fixed. Element 79 represents athin, curved sheet mounted on a lever 71 and a pivot 72 for pivotalmotion. Sections A and C are relatively transparent and section B isrelatively opaque as also indicated in the front view of element 70shown in FIGURE 6. Thus, as member 70' is pivoted, its position can beused to control light transmission and thereby control volume in thesame general manner as previously explained. 1

By making element 76 of an entirely opaque material,

another modification of the invention is shown in FIG- URE 7 in which 80represents such a curved sheet element similar to element 70 but in thiscase having a suitably shaped aperture 81 which can be used to controllight fiow as previously explained. V

In FIGURE 8 each of the photo conductor tubes 30,

31 is fixed and each is illuminated by fixed separate re- Slider 92 mayfor example be controlled by an organ foot pedal such as shown in FIGURE3 which allows a completely remote operation since only the resistor 944 and slider 92 would be required at the site of the foot pedal.

A final variation of the invention is shown in FIGURE 9 in which appearsa series configuration including neon lamps 90, 91 and additional photoconductor tubes 109, 101 between which at 102 is connected a voltagesource 103. The light source 20 is fixed but is reflected on photoconductor tubes 160, 101 by means of a movable mirror 165. The circuitof FIGURE 9 actually employs the invention twice in that potentialdividers based on the inventions teaching exists both between lamps and91 as well as between terminals T and T One potential divider controlsthe other potential divider since illumination of lamps 96 and 91 varywith the position of mirrcr 195. Consequently the voltage in terminal Tvarys with the position of mirror 165. The circuit of FIGURE 9 like thatof FIGURE 8 is thus readily applicable to remote type operation sincemirror 105 could for example be operated by an organ foot pedal.

Nhile various arrangements of photo conductor devices could be employedin plural numbers and in series and parallel networks, it is deemedessential to have at least a pair of such devices across which thepotential can be applied and between which there can be a controllablepotential terminal such as terminal T Furthermore whatever light sourcemeans is employed to illuminate the photo conductor tubes whether asingle or plural source or whether fixed or movable the light sourcemust be proximate the tubes that are being illuminated through themirror concept, for example, of FIGURE 9 gives some latitude in thisregard. By comparing all of the embodiments illustrated, it will also benoted that each is characterized by having a control means whicheffectively controls the light and because of this, the potential at TThus, control means can be the light source itself as in FIGURES 1 and3, the photo conductor device housing as in FIGURE 4, or a movable film,wiper contact or mirror as in FIGURES 5, 8 and 9.

One possible and in some cases ideal resistance variation betweenterminals in a FIGURE 1 type configuration is illustrated in FIGURE 2 bycurves 125, 126 and 127. Curve represents the resistance betweenterminals T and T which, with proper design, can be kept as a relativelyconstant value. Curve 126 represents the resistance between terminals Tand T whereas curve 127 represents the resistance between terminals Tand T Thus, with an appropriately selected design, the resistancebetween terminals T and T can be kept relatively constant whereas theresistance between terminals T and T and between terminals T and T canbe made to vary oppositely as the position of the particular positioncontrol device is changed.

Having described the invention, I claim: 1. In an electric organ, swellcontrol, in combination: (a) a potential divider comprising a pair ofphotoconductor devices connected in electrical series and including apair of end terminals and a center tap terminal; (b) an audio signalvoltage source connected to said end terminals across said divider;

(c) an audio amplifier connected to and having its volume controlled bythe voltage at said center tap;

(d) a foot control for controlling said amplifier volume including apivotly mounted foot pedal;

(e) a light source mounted on and movable with said pedal in an arcuatepath;

(f) housing means supporting said photo-conductor devices one above theother and proximate said path whereby the light therefrom strikes oneand then the other of said devices as said pedal pivots downwardly; and

(g) shading means effective to shade said devices differently such thatas said pedal pivots downwardly the light from said source strikes saiddevices in sequence and in changing quantity to produce a predeterminedchanging voltage at said center tap and thereby control the swell ofsaid volume according to said voltage. I

2. In an electric organ as claimed in claim 1 wherein said devices arepositioned and said shading means is arranged such that as said pedalpivots downwardly the turn-on response time of the lower of said devicespredominates and provides a substantially quick response in said swellcontrol.

3. In an electric organ as claimed in claim 1 wherein said devices,light source and shading means are arranged such that the audio-volumelight source position relation is substantially linear.

References Cited UNITED STATES PATENTS Lord 250209 Corwin 250229 XBostrom et a1. 250-239 Tomasulo et a1 250-211 Gomez 250206 X Thomson250-209 X Thorpe 250-209 Plaisance 250-229 RALPH G. NILSON, PrimaryExaminer.

M. A. LEAVITT, Assistant Examiner.

